1. Field of the Invention
The present invention relates to an apparatus for and a method of controlling the temperature of an exhaust gas sensor disposed in the exhaust passage of an internal combustion engine, and a recording medium storing a program for controlling the temperature of such an exhaust gas sensor.
2. Description of the Related Art
Exhaust gas sensors are often disposed in the exhaust passages of internal combustion engines for detecting a physical quantity as to an exhaust gas component state, such as an exhaust gas component concentration, for the purpose of controlling the operation of the internal combustion engine or monitoring the status of an exhaust gas purifying system. Specifically, an exhaust gas sensor is disposed at a certain location in the exhaust gas passage and has an element sensitive to an exhaust gas component state to be detected, the element being positioned for contact with an exhaust gas flowing through the exhaust passage. For example, an air-fuel ratio sensor such as an O2 sensor or the like is disposed as an exhaust gas sensor upstream or downstream of an exhaust gas purifying catalyst disposed in the exhaust passage for the purpose of controlling the air-fuel ratio of the internal combustion engine in order to keep well the purifying ability of the catalyst.
Some air-fuel ratio sensors have a built-in heater for heating the active element thereof for increasing the temperature of the element and activating the element to enable the element to perform its essential functions and also removing foreign matter deposited on the element. For example, an air-fuel ratio sensor such as an O2 sensor or the like usually has an electric heater for heating the active element thereof. After the internal combustion engine has started to operate, the electric heater is energized to increase the temperature of the active element of the O2 sensor to activate the active element and keep the active element active.
As shown in FIG. 3 of the accompanying drawings, the O2 sensor produces an output voltage Vout which changes with a large gradient with respect to a change in the air-fuel ratio of an exhaust gas, i.e., which is highly sensitive to a change in the air-fuel ratio, only in a small range xcex94 (near a stoichiometric air-fuel ratio) of values of the air-fuel ratio that is represented by an oxygen concentration in the exhaust gas to which the active element is sensitive. A change in the output voltage Vout of the O2 sensor, i.e., a gradient of the output voltage Vout with respect to the air-fuel ratio, is smaller in air-fuel ratio ranges that are richer and leaner than the highly sensitive range xcex94. The output characteristics of the O2 sensor, i.e., the gradient of the highly sensitive range xcex94, etc., vary depending on the temperature of the active element. When the air-fuel ratio is to be controlled using the output voltage from the O2 sensor, therefore, it is desirable to keep the output characteristics of the O2 sensor in a desired range as much as possible and hence to keep the temperature of the active element of the O2 sensor in a desired temperature range as stably as possible for better air-fuel ratio control.
Not only O2 sensors but also Many exhaust gas sensors have their output characteristics affected by the temperature of the active element. If the internal combustion engine is to be controlled using the output signal from the O2 sensor, then it is preferable to keep the temperature of the active element of the exhaust gas sensor in a desired temperature range as stably as possible for better engine control. When the active element of the exhaust gas sensor is heated to clean the active element, it is also preferable to keep the temperature of the active element of the exhaust gas sensor in a desired temperature range for a better cleaning effect.
As disclosed in Japanese laid-open patent publication No. 2000-304721 by the applicant of the present application, it is known to estimate the temperature of the active element of an exhaust gas sensor (an air-fuel ratio sensor in the publication) and control the energization of a heater (an electric heater) based on the estimated temperature for thereby keep the temperature of the active element in a desired temperature range to obtain appropriate output characteristics from the exhaust gas sensor. According to the disclosed arrangement, the resistance of the heater is recognized from detected values of a current flowing through the heater and a voltage applied across the heater, and the temperature of the active element is estimated based on the detected resistance of the heater.
The heater is controlled based on only the estimated temperature of the active element. Consequently, when the operating state of an internal combustion engine changes frequently and hence the temperature of the exhaust gas emitted therefrom changes frequently, it is difficult to keep the temperature of the active element in a desired temperature range stably and reliably. This drawback occurs also if the temperature of the active element is detected by a temperature sensor and the heater is controlled based on the detected temperature.
It is therefore an object of the present invention to provide an apparatus for and a method of controlling the temperature of the active element of an exhaust gas sensor stably in a desired temperature range even if the temperature of an exhaust gas changes.
Another object of the present invention is to provide a recording medium storing a temperature control program controlling the temperature of the active element of an exhaust gas sensor stably in a desired temperature range even if the temperature of an exhaust gas changes.
To achieve the above objects, there is provided in accordance with a first aspect of the present invention an apparatus for controlling the temperature of an exhaust gas sensor disposed in an exhaust passage of an internal combustion engine and having an active element for contacting an exhaust gas flowing through the exhaust passage and a heater for heating the active element, the apparatus comprising exhaust gas temperature estimating means for sequentially estimating the temperature of the exhaust gas flowing through the exhaust passage, using at least a parameter representative of an operating state of the internal combustion engine, and heater control means for controlling the heater to equalize the temperature of the active element of the exhaust gas sensor with a predetermined target temperature, using an estimated value of the temperature of the exhaust gas from the exhaust gas temperature estimating means.
Similarly, there is also provided in accordance with the first aspect of the present invention a method of controlling the temperature of an exhaust gas sensor disposed in an exhaust passage of an internal combustion engine and having an active element for contacting an exhaust gas flowing through the exhaust passage and a heater for heating the active element, the method comprising the steps of sequentially estimating the temperature of the exhaust gas flowing through the exhaust passage, using at least a parameter representative of an operating state of the internal combustion engine, and controlling the heater to equalize the temperature of the active element of the exhaust gas sensor with a predetermined target temperature, using an estimated value of the temperature of the exhaust gas.
There is also provided in accordance with the first aspect of the present invention a recording medium readable by a computer and storing a temperature control program for being executed by the computer for controlling the temperature of an exhaust gas sensor disposed in an exhaust passage of an internal combustion engine and having an active element for contacting an exhaust gas flowing through the exhaust passage and a heater for heating the active element, the temperature control program comprising an exhaust gas temperature estimating program for enabling the computer to carry out a process of sequentially estimating the temperature of the exhaust gas flowing through the exhaust passage, using at least a parameter representative of an operating state of the internal combustion engine, and a heater control program for enabling the computer to carry out a process of controlling the heater to equalize the temperature of the active element of the exhaust gas sensor with a predetermined target temperature, using an estimated value of the temperature of the exhaust gas.
According to the first aspect of the present invention, since the temperature of the exhaust gas is estimated using the parameter representative of the operating state of the internal combustion engine, which is mainly responsible for a change in the temperature of the exhaust gas, the temperature of the exhaust gas can be estimated appropriately. As the heater control means controls the heater of the exhaust gas sensor using the estimated value of the temperature of the exhaust gas, the temperature of the active element of the exhaust gas sensor can be controlled stably at a predetermined target temperature (desired temperature) while reducing the effect of a change in the temperature of the exhaust gas.
With the apparatus according to the first aspect, the heater control means should preferably sequentially acquire data representative of the temperature of the active element of the exhaust gas sensor, sequentially calculate a control input for the heater by adding at least a control input component depending on the temperature of the active element of the exhaust gas sensor and a control input component depending on the estimated value of the temperature of the exhaust gas from the exhaust gas temperature estimating means, and control the heater depending on the calculated control input.
Likewise, with the method according to the first aspect, the step of sequentially estimating the temperature of the exhaust gas should preferably comprise the steps of sequentially estimating the temperature of the exhaust gas in the vicinity of an exhaust port of the internal combustion engine based on the parameter representative of the operating state of the internal combustion engine, and estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor, using at least an estimated value of the temperature of the exhaust gas in the vicinity of the exhaust port and data representative of the speed of the exhaust gas.
With the recording medium according to the first aspect, the computer control program should preferably comprise a program for enabling the computer to carry out a process of sequentially acquiring data representative of the temperature of the active element of the exhaust gas sensor, sequentially calculating a control input for the heater by adding at least a control input component depending on the temperature of the active element of the exhaust gas sensor and a control input component depending on the estimated value of the temperature of the exhaust gas, and controlling the heater depending on the calculated control input.
By thus calculating the control input so as to include a control input component depending on the temperature of the active element of the exhaust gas sensor, i.e., a feedback component, and a control input component depending on the estimated or detected value of the temperature of the exhaust gas, i.e., a feed-forward component depending on the temperature of the exhaust gas, it is possible to control the temperature of the active element of the exhaust gas sensor stably at the target temperature. Since the control input for the heater includes a feed-forward component depending on the temperature of the exhaust gas, the effect of a change in the temperature of the exhaust gas can be compensated for to stabilize the temperature of the active element.
While the data representative of the temperature of the active element may be data directly detected by a temperature sensor attached to the active element, i.e., a detected value of the temperature of the active element, the temperature of the active element may be estimated according to a suitable algorithm which takes into account a heat transfer between the heater and the active element, a heat transfer between the active element and the exhaust gas, etc., and the estimated value may be used as the data representative of the temperature of the active element. The control input may also include, in addition to the above control input components, a component depending on the temperature of the heater and a component depending on the target temperature for the active element. The control input component depending on the temperature of the active element may be a control input component depending on the difference between the temperature of the active element and the target temperature.
With the apparatus according to the first aspect, the temperature of the exhaust gas which is estimated by the exhaust gas temperature estimating means should preferably include at least the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor, and the heater control means should preferably use the estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor in order to control the heater.
Likewise, with the method according to the first aspect, the temperature of the exhaust gas which is estimated should preferably include at least the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor, and the estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor should preferably be used in order to control the heater.
With the recording medium according to the first aspect, the temperature of the exhaust gas which is estimated should preferably include at least the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor, and the heater control program should preferably comprise a program for enabling the computer to carry out a process of using the estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor in order to control the heater.
According to the present invention as described above, the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor, i.e., the temperature of the exhaust gas which directly affects the temperature of the active element of the exhaust gas sensor, is sequentially estimated. By using the estimated value for the control of the heater, it is possible to control the temperature of the active element of the exhaust gas sensor more stably at the target temperature.
The inventors"" knowledge shows that the temperature of the exhaust gas in the vicinity of the exhaust port of the internal combustion engine, i.e., the temperature of the exhaust gas in the vicinity of the inlet of the exhaust passage, is closely correlated to the operating state of the internal combustion engine. It is therefore possible to estimate the temperature of the exhaust gas in the vicinity of the exhaust port with relatively high accuracy based on the parameter representative of the operating state of the internal combustion engine.
The exhaust gas sensor is often located in a position that is spaced a certain distance downstream from the exhaust port of the internal combustion engine. At each point of time, the exhaust gas present in the exhaust port reaches the location of the exhaust gas sensor with a time lag or delay depending on the speed of the exhaust gas. Stated otherwise, at each point of time, the temperature of the exhaust gas in the vicinity of the exhaust port generally does not affect the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor at the same point of time, but affects the temperature in the vicinity of the location of the exhaust gas sensor after elapse of a time depending on the speed of the exhaust gas. The time lag or delay specifically depends on the distance between the exhaust port and the location of the exhaust gas sensor in the direction in which the exhaust gas flows, and the speed of the exhaust gas. The distance between the exhaust port and the location of the exhaust gas sensor is of a constant value.
With the apparatus according to the first aspect, the exhaust gas temperature estimating means should preferably sequentially estimate the temperature of the exhaust gas in the vicinity of an exhaust port of the internal combustion engine based on the parameter representative of the operating state of the internal combustion engine, and estimate the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor, using at least an estimated value of the temperature of the exhaust gas and data representative of the speed of the exhaust gas. With the method according to the first aspect, similarly, the above process of the exhaust gas temperature estimating means should preferably be carried out by the step of sequentially estimating the temperature of the exhaust gas. With the recording medium according to the first aspect, the exhaust gas temperature estimating program should preferably be a program for enabling the computer to carry out the above process of the exhaust gas temperature estimating means.
It is thus possible to properly estimate the temperature of the exhaust gas from time to time in the vicinity of the location of the exhaust gas sensor, taking into account the time lag required for the exhaust gas to reach the location of the exhaust gas sensor from the exhaust port of the internal combustion engine. By controlling the heater with the estimated value of the temperature of the exhaust gas, the active element of the exhaust gas sensor can be controlled better in temperature.
Though the data representative of the speed of the exhaust gas may be provided by a detected value produced by a flow sensor, the data may be provided by a value estimated from detected data of the rotational speed and the intake pressure (the pressure in the intake pipe) of the internal combustion engine. If the exhaust sensor is positioned in the vicinity of the exhaust port of the internal combustion engine, then the estimated value of the temperature of the exhaust gas in the vicinity of the exhaust port based on the operating state of the internal combustion engine may directly be used as the estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor.
The correlation between the operating state of the internal combustion engine and the temperature of the exhaust gas in the vicinity of the exhaust port is high particularly in a steady operating state of the internal combustion engine, i.e., an operating state where the rotational speed is constant. However, when the operating state of the internal combustion engine changes, the temperature of the exhaust gas in the vicinity of the exhaust port tends to suffer a transient variation due to a heat exchange between the exhaust gas and an object near the exhaust port of the internal combustion engine.
With the apparatus according to the first aspect for estimating the temperature of the exhaust gas in the vicinity of the exhaust port, the exhaust gas temperature estimating means should preferably sequentially determine a basic value of the temperature of the exhaust gas (which corresponds to an estimated value of the temperature of the exhaust gas in the vicinity of the exhaust port under a steady operating state of the internal combustion engine) based on a preset correlation between the parameter and the temperature of the exhaust gas from the parameter representative of the operating state of the internal combustion engine, and determine a value which follows the basic value with a response delay, as the estimated value of the temperature of the exhaust gas in the vicinity of the exhaust port. With the method according to the first aspect, similarly, the above process of the exhaust gas temperature estimating means should preferably be carried out by the step of sequentially estimating the temperature of the exhaust gas. With the recording medium according to the first aspect, the exhaust gas temperature estimating program should preferably be a program for enabling the computer to carry out the above process of the exhaust gas temperature estimating means.
According to the above arrangement, the accuracy of the estimated value of the temperature of the exhaust gas in the vicinity of the exhaust port of the internal combustion engine can be increased, and hence the accuracy of the estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor can be increased.
The temperature of the exhaust gas in the vicinity of the exhaust port is highly correlated to the rotational speed of the internal combustion engine and the amount of intake air introduced into the internal combustion engine (the amount of intake air introduced into the internal combustion engine per unit time). Therefore, the parameter representative of the operating state of the internal combustion engine which is used to estimate the temperature of the exhaust gas in the vicinity of the exhaust port should preferably include at least a parameter representative of the rotational speed of the internal combustion engine and a parameter representative of an amount of intake air introduced into the internal combustion engine.
In estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor using the estimated value of the temperature of the exhaust gas in the vicinity of the exhaust port of the internal combustion engine and the data representative of the speed of the exhaust gas, if the location of the exhaust gas sensor is widely spaced from the exhaust port, then the temperature of the exhaust gas ranging from the exhaust port to the location of the exhaust gas sensor is generally of a temperature distribution having non-monotonous changes in the direction in which the exhaust gas flows, i.e., a temperature distribution of staggering temperature changes along the direction in which the exhaust gas flows, as the operating state of the internal combustion engine varies. The temperature of the exhaust gas from time to time in each section of the exhaust passage basically depends on the temperature of the exhaust gas that is present upstream of that section in an immediately prior time and the speed of the exhaust gas. In order to sequentially estimate with accuracy the temperature of the exhaust gas at a certain location in the exhaust passage, therefore, it is preferable to sequentially recognize the temperature of the exhaust gas at a location which is slightly spaced upstream from that location. The temperature of the exhaust gas at a location that is slightly spaced downstream from the exhaust port of the internal combustion engine basically depends on the temperature of the exhaust gas in the vicinity of the exhaust port and the speed of the exhaust gas.
With the apparatus according to the first aspect of the present invention, the exhaust passage from the exhaust port to a position in the vicinity of the location of the exhaust gas sensor is divided into a plurality of partial exhaust passageways along the direction in which the exhaust gas flows. The exhaust gas temperature estimating means should preferably comprise means for estimating the temperature of the exhaust gas in a most upstream one of the partial exhaust passageways using the estimated value of the temperature of the exhaust gas in the vicinity of the exhaust port and the data representative of the speed of the exhaust gas, estimating the temperatures of the exhaust gas in the partial exhaust passageways other than the most upstream partial exhaust passageway using estimated values of the temperatures of the exhaust gas in adjacent partial exhaust passageways upstream thereof and the data representative of the speed of the exhaust gas, and obtaining an estimated value of the temperature of the exhaust gas in a most downstream one of the partial exhaust passageways as the estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor. With the method according to the first aspect, similarly, the above process of the exhaust gas temperature estimating means should preferably be carried out by the step of sequentially estimating the temperature of the exhaust gas. With the recording medium according to the first aspect, the exhaust gas temperature estimating program should preferably be a program for enabling the computer to carry out the above process of the exhaust gas temperature estimating means.
With the above arrangement, the temperatures of the exhaust gas in the respective partial exhaust passageways between a position in the vicinity of the exhaust port of the internal combustion engine and a position in the vicinity of the location of the exhaust gas sensor can successively be determined accurately. By obtaining the estimated value of the temperature of the exhaust gas in the most downstream one of the partial exhaust passageways as the estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor, the accuracy of the estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor can be increased.
To achieve the above object, there is provided in accordance with a second aspect of the present invention an apparatus for controlling the temperature of an exhaust gas sensor disposed in an exhaust passage of an internal combustion engine and having an active element for contacting an exhaust gas flowing through the exhaust passage and a heater for heating the active element, the apparatus comprising an exhaust gas temperature sensor disposed in the exhaust passage for detecting the temperature of the exhaust gas flowing through the exhaust passage, and heater control means for controlling the heater to equalize the temperature of the active element of the exhaust gas sensor with a predetermined target temperature, using a detected value of the temperature of the exhaust gas from the exhaust gas temperature sensor.
Similarly, there is also provided in accordance with the second aspect of the present invention a method of controlling the temperature of an exhaust gas sensor disposed in an exhaust passage of an internal combustion engine and having an active element for contacting an exhaust gas flowing through the exhaust passage and a heater for heating the active element, the method comprising the steps of detecting the temperature of the exhaust gas flowing through the exhaust passage with an exhaust gas temperature sensor disposed in the exhaust passage, and controlling the heater to equalize the temperature of the active element of the exhaust gas sensor with a predetermined target temperature, using a detected value of the temperature of the exhaust gas.
There is also provided in accordance with the second aspect of the present invention a recording medium readable by a computer and storing a temperature control program for being executed by the computer for controlling the temperature of an exhaust gas sensor disposed in an exhaust passage of an internal combustion engine and having an active element for contacting an exhaust gas flowing through the exhaust passage and a heater for heating the active element, the temperature control program comprising a heater control program for enabling the computer to carry out a process of controlling the heater to equalize the temperature of the active element of the exhaust gas sensor with a predetermined target temperature, using a detected value of the temperature of the exhaust gas from an exhaust gas sensor which is disposed in the exhaust passage to detect the temperature of the exhaust gas.
According to the second aspect of the present invention, since the heater of the exhaust gas sensor is controlled using the detected value of the temperature of the exhaust gas from the exhaust gas temperature sensor, the temperature of the active element of the exhaust gas sensor can be controlled stably at a predetermined target temperature (desired temperature) while reducing the effect of a change in the temperature of the exhaust gas.
In a preferred configuration of the apparatus, the method, and the recording medium according to the second aspect, the exhaust gas temperature sensor is disposed in the vicinity of the active element of the exhaust gas sensor. Stated otherwise, the detected value of the temperature of the exhaust gas is from the exhaust gas temperature sensor which is disposed in the vicinity of the active element of the exhaust gas sensor.
The temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor, i.e., the temperature of the exhaust gas which directly affects the temperature of the active element of the exhaust gas sensor, is detected by the exhaust gas temperature sensor. By using the detected value for the control of the heater, it is possible to control the temperature of the active element of the exhaust gas sensor more stably at the target temperature.
With the apparatus according to the first aspect where the exhaust gas temperature sensor is disposed in the vicinity of the location of the active element of the exhaust gas sensor, the heater control means should preferably sequentially acquire data representative of the temperature of the active element of the exhaust gas sensor, sequentially calculate a control input for the heater by adding at least a control input component depending on the temperature of the active element of the exhaust gas sensor and a control input component depending on the detected value of the temperature of the exhaust gas from the exhaust gas temperature sensor, and control the heater depending on the calculated control input. With the method according to the second aspect, similarly, the above process of the heater control means should preferably be carried out when the heater is controlled. With the recording medium according to the second aspect, the heater control program should preferably be a program for enabling the computer to carry out the above process of the heater control means.
Since a control input for the heater includes a control input component depending on the temperature of the active element of the exhaust gas sensor (a feedback component), and a control input component depending on the detected value of the temperature of the exhaust gas (a feed-forward component), it is possible to control the temperature of the active element of the exhaust gas sensor stably at the target temperature as described above with respect to the control of the heater according to the first aspect.
In the exhaust system of an internal combustion engine, an exhaust gas temperature sensor may be disposed in a certain location in the exhaust passage for a purpose different from the control of the temperature of the active element of the exhaust gas sensor, e.g., a purpose of recognizing the state of an exhaust gas purifying apparatus. The exhaust gas temperature sensor is not necessarily disposed in the vicinity of the location of the exhaust gas sensor, but is often disposed in a location spaced from the exhaust gas sensor in the direction of a flow of the exhaust gas in the exhaust passage.
With the apparatus according to the second aspect of the present invention, if the exhaust gas temperature sensor is disposed in the exhaust passage in spaced relation to the exhaust gas sensor, then the apparatus should preferably comprise exhaust gas temperature estimating means for sequentially estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor using the detected value of the temperature of the exhaust gas from the exhaust gas temperature sensor, and the heater control means should preferably comprise means for controlling the heater using an estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor, rather than the detected value of the temperature of the exhaust gas.
Likewise, with the method according to the second aspect of the present invention, if the exhaust gas temperature sensor is disposed in the exhaust passage in spaced relation to the exhaust gas sensor, then the method should preferably comprise the step of sequentially estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor using the detected value of the temperature of the exhaust gas, and the step of controlling the heater should preferably comprise the step of controlling the heater using an estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor, rather than the detected value of the temperature of the exhaust gas.
With the recording medium according to the second aspect of the present invention, if the exhaust gas temperature sensor is disposed in the exhaust passage in spaced relation to the exhaust gas sensor, then the temperature control program should preferably further comprise an exhaust gas temperature estimating program for enabling the computer to carry out a process of sequentially estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor using the detected value of the temperature of the exhaust gas from the exhaust gas temperature sensor, and the heater control program should preferably comprise a program for controlling the heater using an estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor, rather than the detected value of the temperature of the exhaust gas.
According to the above inventive features, since the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor is estimated using the detected value of the temperature of the exhaust gas from the exhaust gas temperature sensor, the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor can appropriately be recognized without the need for another exhaust gas temperature sensor disposed in the vicinity of the location of the exhaust gas sensor. By controlling the heater of the exhaust gas sensor using the estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor, it is possible to control the temperature of the active element of the exhaust gas sensor stably at a predetermined temperature.
If the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor is estimated using the detected value of the temperature of the exhaust gas as described above, then the temperature of the active element of the exhaust gas sensor can be controlled stably at the target temperature by calculating the control input in the same manner as with the first aspect and controlling the heater depending on the control input.
In determining the estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor using the detected value of the temperature of the exhaust gas, if the exhaust gas temperature sensor is positioned upstream of the exhaust gas sensor, then the exhaust gas present in the location of the exhaust gas sensor at each point of time reaches the location of the exhaust gas sensor with a time lag or delay depending on the speed of the exhaust gas. If the exhaust gas temperature sensor is positioned downstream of the exhaust gas sensor, then the exhaust gas present in the location of the exhaust gas sensor at each point of time reaches the location of the exhaust gas temperature sensor with a time lag or delay depending on the speed of the exhaust gas.
Therefore, with the apparatus according to the second aspect which has the exhaust gas temperature estimating means, the exhaust gas temperature estimating means should preferably comprise means for estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor using at least the detected value of the temperature of the exhaust gas from the exhaust gas temperature sensor and data representative of the speed of the exhaust gas. Similarly, with the method according to the second aspect which carries out the step of estimating the temperature of the exhaust gas, the process of the above exhaust gas temperature estimating means should preferably be carried out by the step of estimating the temperature of the exhaust gas. With the recording medium according to the second aspect which stores the exhaust gas temperature estimating program, the exhaust gas temperature estimating program should preferably be a program for enabling the computer to carry out the process of the exhaust gas temperature estimating means.
It is thus possible to properly estimate the temperature of the exhaust gas from time to time in the vicinity of the location of the exhaust gas sensor, taking into account a time lag or delay caused until the exhaust gas reaches a downstream one of the exhaust gas temperature sensor and the exhaust gas sensor from the downstream sensor. The temperature of the active element of the exhaust gas sensor can well be controlled by controlling the heater using the estimated value of the temperature of the exhaust gas.
In the description of the present invention which follows, the apparatus according to the second aspect refers to an apparatus including the exhaust gas temperature estimating means unless stated otherwise. Similarly, in the description of the present invention which follows, the method according to the second aspect includes the step of estimating the temperature of the exhaust gas, and the recording medium according to the second aspect includes the exhaust gas temperature estimating program.
In the second aspect of the present invention which estimates the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor, if the exhaust gas temperature sensor and the exhaust gas sensor are relatively widely spaced from each other, then it is preferable to apply the same idea as if the exhaust passage from the exhaust port of the internal combustion engine to the location of the exhaust gas sensor is divided into a plurality of partial exhaust passageways according to the first aspect.
Specifically, with the apparatus according to the second aspect, the exhaust passage from a position in the vicinity of the location of the exhaust gas temperature sensor to a position in the vicinity of the location of the exhaust gas sensor is divided into a plurality of partial exhaust passageways along the direction in which the exhaust gas flows. The exhaust gas temperature estimating means should preferably comprise means for estimating the temperature of the exhaust gas in one of the partial exhaust passageways which is closest to the exhaust gas temperature sensor using the detected value of the temperature of the exhaust gas from the exhaust gas temperature sensor and data representative of the speed of the exhaust gas, estimating the temperatures of the exhaust gas in the partial exhaust passageways other than the partial exhaust passageway which is closest to the exhaust gas temperature sensor using the estimated value of the temperature of the exhaust gas in the partial exhaust passageway which is adjacent to the partial exhaust passageways on the side of the exhaust gas temperature sensor and data representative of the speed of the exhaust gas, and acquiring the temperature of the exhaust gas in the partial exhaust passageway which is closest to the exhaust gas sensor as the estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor.
Similarly, with the method according to the second aspect, it is preferable for the same process as the process of the exhaust gas temperature estimating means to be carried out by the step of estimating the temperature of the exhaust gas to obtain the estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor. Similarly, with the recording medium according to the second aspect, it is preferable for the exhaust gas temperature estimating program to be a program for enabling the computer to carry out the same process as the process of the exhaust gas temperature estimating means.
According to the above inventive features, it is possible to determine successively with accuracy the temperatures of the exhaust gas in the respective partial exhaust passageways between the position in the vicinity of the location of the exhaust gas temperature sensor and the position in the vicinity of the location of the exhaust gas sensor, starting from the position in the vicinity of the location of the exhaust gas temperature sensor. The accuracy of the estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor by obtaining the estimated value of the temperature of the exhaust gas in the partial exhaust passageway closest to the exhaust gas sensor, as the estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor.
With the apparatus according to the first and second aspects which estimate the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor as described above, the exhaust gas temperature estimating means should preferably comprise means for estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor according to an estimating algorithm which is constructed taking into account at least a heat transfer between a passage-defining member which defines the exhaust passage from a position in the vicinity of the location of the exhaust gas sensor to a position in the vicinity of the exhaust gas temperature sensor and the exhaust gas flowing through the passage-defining member.
Particularly, with the apparatus according to the first aspect, the exhaust gas temperature estimating means should preferably comprise means for estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor according to an estimating algorithm which is constructed taking into account at least a heat transfer between a passage-defining member which defines the exhaust passage upstream of a position in the vicinity of the location of the exhaust gas sensor and the exhaust gas flowing through the passage-defining member. Similarly, with the apparatus according to the second aspect, the exhaust gas temperature estimating means should preferably comprise means for estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor according to an estimating algorithm which is constructed taking into account at least a heat transfer between a passage-defining member which defines the exhaust passage from a position in the vicinity of the location of the exhaust gas sensor to a position in the vicinity of the exhaust gas temperature sensor and the exhaust gas flowing through the passage-defining member.
With any of the apparatus according to the first and second aspects of the present invention, for estimating the temperatures of the exhaust gas in the respective partial exhaust passageways as described above, the exhaust gas temperature estimating means should preferably comprise means for estimating the temperatures of the exhaust gas in the partial exhaust passageways according to an estimating algorithm which is constructed taking into account at least a heat transfer between passage-defining members which define the partial exhaust passageways and the exhaust gas flowing through the passage-defining members.
Specifically, when the exhaust gas flows through the exhaust passage, a heat transfer occurs between the passage-defining member which defines the exhaust passage and the exhaust gas, and affects the temperature of the exhaust gas. The accuracy of the estimated value of the temperature of the exhaust gas can thus be increased by estimating the temperature of the exhaust gas according to an estimating algorithm which takes into account at least a heat transfer between the exhaust gas and the passage-defining member through which the exhaust gas flows.
The heat transfer between the passage-defining member and the exhaust gas should preferably be taken into account also in the method and the recording medium according to the present invention. More specifically, with the methods according to the first and second aspects of the present invention, it is preferable for the same process as the process of the exhaust gas temperature estimating means, i.e., the process of estimating the temperature of the exhaust gas according to the estimating algorithm which takes the heat transfer into account, to be carried out by the step of estimating the temperature of the exhaust gas. Similarly, with the recording mediums according to the first and second aspects, the exhaust gas temperature estimating program should preferably be a program for enabling the computer to carry out the same process as the process of the exhaust gas temperature estimating means.
With the apparatus according to the first and second aspects which estimate the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor, the exhaust gas temperature estimating means should preferably comprise means for estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor according to an estimating algorithm which is constructed taking into account at least a heat radiation from a passage-defining member which defines the exhaust passage in the vicinity of the location of the exhaust gas sensor, into the atmosphere outside of the passage-defining member. More preferably, the exhaust gas temperature estimating means should comprise means for estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor according to an estimating algorithm which is constructed taking into account at least a heat transfer between a passage-defining member which defines the exhaust passage in the vicinity of the location of the exhaust gas sensor and the exhaust gas flowing through the passage-defining member and a heat radiation from the passage-defining member into the atmosphere outside of the passage-defining member.
With the apparatus according to the first aspect of the present invention, the exhaust gas temperature estimating means should preferably comprise, in particular, means for estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor according to an estimating algorithm which is constructed taking into account at least a heat radiation from a passage-defining member which defines the exhaust passage upstream of a position in the vicinity of the location of the exhaust gas sensor, into the atmosphere outside of the passage-defining member. More preferably, the exhaust gas temperature estimating means should comprise means for estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor according to an estimating algorithm which is constructed taking into account at least a heat transfer between a passage-defining member which defines the exhaust passage upstream of a position in the vicinity of the location of the exhaust gas sensor and the exhaust gas flowing through the passage-defining member and a heat radiation from the passage-defining member into the atmosphere outside of the passage-defining member.
Likewise, with the apparatus according to the second aspect of the present invention, the exhaust gas temperature estimating means should preferably comprise means for estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor according to an estimating algorithm which is constructed taking into account at least a heat radiation from a passage-defining member which defines the exhaust passage from a position in the vicinity of the location of the exhaust gas sensor to a position in the vicinity of the exhaust gas temperature sensor, into the atmosphere outside of the passage-defining member, or more preferably, an estimating algorithm which is constructed taking into account at least a heat transfer between a passage-defining member which defines the exhaust passage from a position in the vicinity of the location of the exhaust gas sensor to a position in the vicinity of the exhaust gas temperature sensor and the exhaust gas flowing through the passage-defining member, and a heat radiation from the passage-defining member into the atmosphere outside of the passage-defining member.
With any of the apparatus according to the first and second aspects of the present invention, for estimating the temperatures of the exhaust gas in the respective partial exhaust passageways as described above, the exhaust gas temperature estimating means should preferably comprise means for estimating the temperatures of the exhaust gas in the partial exhaust passageways according to an estimating algorithm which is constructed taking into account at least a heat radiation from passage-defining members which define the partial exhaust passageways into the atmosphere outside of the passage-defining members, or more preferably an estimating algorithm which is constructed taking into account a heat transfer between passage-defining members which define the partial exhaust passageways and the exhaust gas flowing through the passage-defining members, and the above heat radiation.
Specifically, when the exhaust gas flows through the exhaust passage, a heat radiation occurs from the passage-defining member which defines the exhaust passage into the atmosphere, and affects the temperature of the exhaust gas. The accuracy of the estimated value of the temperature of the exhaust gas can thus be increased by estimating the temperature of the exhaust gas according to an estimating algorithm which takes into account at least a heat radiation from the passage-defining member through which the exhaust gas flows into the atmosphere. In particular, the accuracy of the estimated value of the temperature of the exhaust gas can effectively be increased if the heat transfer between the exhaust gas and the passage-defining member is also taken into account.
The heat radiation from the passage-defining member into the atmosphere should preferably be taken into account also in the method and the recording medium according to the present invention. More specifically, with the methods according to the first and second aspects of the present invention, it is preferable for the same process as the process of the exhaust gas temperature estimating means, i.e., the process of estimating the temperature of the exhaust gas according to the estimating algorithm which takes the heat radiation into account (more preferably the estimating algorithm which takes the heat radiation and the heat transfer into account, to be carried out by the step of estimating the temperature of the exhaust gas. Similarly, with the recording mediums according to the first and second aspects, the exhaust gas temperature estimating program should preferably be a program for enabling the computer to carry out the same process as the process of the exhaust gas temperature estimating means.
With the apparatus according to the first aspect of the present invention, if the exhaust passage upstream of a position in the vicinity of the location of the exhaust gas sensor includes a catalyst for purifying the exhaust gas, as a passage-defining member which defines a portion of the exhaust passage, then the exhaust gas temperature estimating means should preferably comprise means for estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor according to an estimating algorithm which is constructed taking into account at least heating of the catalyst. Similarly, with the apparatus according to the second aspect of the present invention, if the exhaust passage from a position in the vicinity of the location of the exhaust gas sensor to a position in the vicinity of the exhaust gas temperature sensor includes a catalyst for purifying the exhaust gas, as a passage-defining member which defines a portion of the exhaust passage, then the exhaust gas temperature estimating means should preferably comprise means for estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor according to an estimating algorithm which is constructed taking into account at least heating of the catalyst. It is more preferable to estimate the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor according to an estimating algorithm which takes into account not only heating of the catalyst, but also the heat transfer between the passage-defining member and the exhaust gas and the heat transfer from the passage-defining member into the atmosphere.
With any of the apparatus according to the first and second aspects of the present invention, for estimating the temperatures of the exhaust gas in the respective partial exhaust passageways as described above, if at least one of the partial exhaust passageways includes a catalyst for purifying the exhaust gas, as a passage-defining member which defines a portion of the exhaust passage, then the exhaust gas temperature estimating means should preferably comprise means for estimating the temperature of the exhaust gas in the partial exhaust passageway which includes the catalyst according to an estimating algorithm which is constructed taking into account at least heating of the catalyst. More preferably, the exhaust gas temperature estimating means should comprise means for estimating the temperature of the exhaust gas in the partial exhaust passageway which includes the catalyst according to an estimating algorithm which is constructed taking into account not only heating of the catalyst, but also a heat transfer between a passage-defining member which defines the partial exhaust passageway and the exhaust gas flowing through the passage-defining member, and a heat radiation from the passage-defining member into the atmosphere outside of the passage-defining member, and estimating the temperature of the exhaust gas in one of the partial exhaust passageways which does not include the catalyst according to an estimating algorithm which is constructed taking into account at least a heat transfer between a passage-defining member which defines the one partial exhaust passageway and the exhaust gas flowing through the passage-defining member, and a heat radiation from the passage-defining member into the atmosphere outside of the passage-defining member.
Specifically, the catalyst for purifying the exhaust gas is heated by its action to purify the exhaust gas (an oxidizing/reducing action), and the heating of the catalyst affects the temperature of the exhaust gas. Therefore, the accuracy of the estimated value of the temperature of the exhaust gas can be increased by estimating the temperature of the exhaust gas according to an estimating algorithm which takes heating of the catalyst into account. Particularly, the accuracy of the estimated value of the temperature of the exhaust gas can effectively be increased if the heat transfer between the exhaust gas and the passage-defining member and the heat radiation from the passage-defining member into the atmosphere are also taken into account.
The heating of the catalyst should preferably be taken into account also in the method and the recording medium according to the present invention. More specifically, with the methods according to the first and second aspects of the present invention, it is preferable for the same process as the process of the exhaust gas temperature estimating means, i.e., the process of estimating the temperature of the exhaust gas according to the estimating algorithm which takes the heating of the catalyst into account (more preferably the estimating algorithm which takes the heating of the catalyst, the heat transfer, and the heat radiation into account, to be carried out by the step of estimating the temperature of the exhaust gas. Similarly, with the recording mediums according to the first and second aspects, the exhaust gas temperature estimating program should preferably be a program for enabling the computer to carry out the same process as the process of the exhaust gas temperature estimating means.
With the apparatus according to the first and second aspects of the present invention, for estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor taking into account the heat transfer between the exhaust gas and the passage-defining member, the exhaust gas temperature estimating means should preferably comprise means for sequentially acquiring at least data representative of the temperature of a passage-defining member which defines the exhaust passage in the vicinity of the location of the exhaust gas sensor, and estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor using the data representative of the temperature of the passage-defining member. The above arrangement holds true for the methods according to the first and second aspects, and the same process as the process of the exhaust gas temperature estimating means should preferably be carried out by the step of estimating the temperature of the exhaust gas. Similarly, with the recording mediums according to the first and second aspects, the exhaust gas temperature estimating program should preferably be a program for enabling the computer to carry out the same process as the process of the exhaust gas temperature estimating means.
By thus sequentially acquiring data representative of the temperature of the passage-defining member which defines the exhaust passage in the vicinity of the location of the exhaust gas sensor, and estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor using the data, the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor can be estimated in a manner taking into account a change in the temperature of the exhaust gas due to the heat transfer between the passage-defining member and the exhaust gas in the vicinity of the location of the exhaust gas sensor, and the accuracy of the estimated value can be increased.
With the apparatus according to the first and second aspects of the present invention, for estimating the temperatures of the exhaust gas in the respective partial exhaust passageways as described above, the exhaust gas temperature estimating means should preferably comprise means for sequentially acquiring data representative of the temperatures of passage-defining members which define the partial exhaust passageways, and estimating the temperatures of the exhaust gas in the partial exhaust passageways using the data representative of the temperatures of the passage-defining members. The above arrangement holds true for the methods according to the first and second aspects, and the same process as the process of the exhaust gas temperature estimating means should preferably be carried out by the step of estimating the temperature of the exhaust gas. Similarly, with the recording mediums according to the first and second aspects, the exhaust gas temperature estimating program should preferably be a program for enabling the computer to carry out the same process as the process of the exhaust gas temperature estimating means.
Thus, the temperatures of the exhaust gas in the respective partial exhaust passageways can be estimated in a manner taking into account a change in the temperature of the exhaust gas due to the heat transfer between the passage-defining members which define the respective partial exhaust passageways and the exhaust gas, and the accuracy of the estimated values can be increased. As a result, the accuracy of the estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor can also be increased.
The data representative of the temperature of the passage-defining member may be detected by a temperature sensor or may be estimated appropriately from other parameters or the like.
With the apparatus according to the first and second aspects of the present invention, for estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor using the data representative of the temperature of the passage-defining member in the vicinity of the location of the exhaust gas sensor, more specifically, the exhaust gas temperature estimating means should preferably comprise means for sequentially determining a change in the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor based on a thermal model in which a change per predetermined time in the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor is expressed as at least the sum of a temperature change component depending on a temperature gradient in the direction in which the exhaust gas flows in the vicinity of the location of the exhaust gas sensor and the speed of the exhaust gas, and a temperature change component depending on the difference between the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor and the temperature of the passage-defining member, and estimating the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor by cumulatively adding the determined change in the temperature to an initial value set when the internal combustion engine has started to operate. The above arrangement holds true for the methods according to the first and second aspects, and the same process as the process of the exhaust gas temperature estimating means should preferably be carried out by the step of estimating the temperature of the exhaust gas. Similarly, with the recording mediums according to the first and second aspects, the exhaust gas temperature estimating program should preferably be a program for enabling the computer to carry out the same process as the process of the exhaust gas temperature estimating means.
For estimating the temperatures of the exhaust gas in the respective partial exhaust passageways using the data representative of the temperatures of the passage-defining members which define the respective partial exhaust passageways, the exhaust gas temperature estimating means should preferably comprise means for sequentially determining changes in the temperature of the exhaust gas in the partial exhaust passageways based on a thermal model in which changes per predetermined time in the temperatures of the exhaust gas in the partial exhaust passageways are expressed as at least the sum of temperature change components depending on temperature gradients in the direction in which the exhaust gas flows in the partial exhaust passageways and the speed of the exhaust gas, and temperature change components depending on the difference between the temperatures of the exhaust gas in the partial exhaust passageways and the temperatures of the passage-defining members which defines the partial exhaust passageways, and estimating the temperatures of the exhaust gas in the partial exhaust passageways by cumulatively adding the determined changes in the temperature to initial values set for the respective partial exhaust passageways when the internal combustion engine has started to operate. The above arrangement holds true for the methods according to the first and second aspects, and the same process as the process of the exhaust gas temperature estimating means should preferably be carried but by the step of estimating the temperature of the exhaust gas. Similarly, with the recording mediums according to the first and second aspects, the exhaust gas temperature estimating program should preferably be a program for enabling the computer to carry out the same process as the process of the exhaust gas temperature estimating means.
In the thermal model, a temperature change component depending on a temperature gradient in the direction in which the exhaust gas flows and the speed of the exhaust gas refers to a temperature change component of the exhaust gas (a temperature change component in a location to be handled in the thermal model) which is caused as the exhaust gas whose temperature is not constant in the direction in which the exhaust gas flows (primarily due to a change in the operating state of the internal combustion engine). A temperature change component depending on the difference between the temperature of a passage-defining member and the temperature of the exhaust gas refers to a temperature change component of the exhaust gas (a temperature change component in a location to be handled in the thermal model) which is caused by a heat transfer between the passage-defining member and the exhaust gas. Therefore, a change per given time in the temperature of the exhaust gas can accurately be determined based on the thermal model. It is then possible to determine an estimated value of the temperature of the exhaust gas with high accuracy by cumulatively adding the change in the temperature of the exhaust gas to an initial model that has been set at the time the internal combustion engine has started to operate, i.e., a predicted value of the temperature of the exhaust gas in a location to be handled in the thermal model at the time the internal combustion engine has started to operate. The temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor can hence be estimated accurately.
With respect to a temperature gradient of the exhaust gas which is required to determine a change per given time in the temperature of the exhaust gas based on the thermal model, if the exhaust sensor is disposed in a position downstream of and relatively close to the exhaust port of the internal combustion engine according to the first aspect of the present invention, then a temperature gradient of the exhaust gas in the vicinity of the location of the exhaust gas sensor can be determined from the latest estimated value (the latest one of already determined values) of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor and the latest estimated value (the latest one of already determined values) of the temperature of the exhaust gas at the exhaust port. Similarly, according to the second aspect of the present invention, if the exhaust sensor is disposed in a position relatively close to the exhaust gas temperature sensor, then a temperature gradient of the exhaust gas in the vicinity of the location of the exhaust gas sensor can be determined from the latest estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor and the latest detected value of the temperature of the exhaust gas from the exhaust gas temperature sensor.
If the temperatures of the exhaust gas in the respective partial exhaust passageways are estimated according to the first aspect of the present invention, then temperature gradients of the exhaust gas in the partial exhaust passageways can be determined from the latest estimated values of the temperatures of the exhaust gas in the partial exhaust passageways and the latest estimated values of the temperatures of the exhaust gas in adjacent ones of the partial exhaust passageways. This arrangement also holds true for the estimation of the temperatures of the exhaust gas in the respective partial exhaust passageways according to the second aspect of the present invention.
A temperature change component depending on the difference between the temperature of a passage-defining member and the temperature of the exhaust gas can be determined from the latest value of data representative of the temperature of the passage-defining member and the latest estimated value of the temperature of the exhaust gas.
With the apparatus according to the first and second aspects of the present invention which employ the data representative of the temperature of the passage-defining member for estimating the temperature of the exhaust gas, the exhaust gas temperature estimating means should preferably comprise means for sequentially estimating the temperature of the passage-defining member using at least the estimated value of the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor and data representative of an atmospheric temperature outside of the passage-defining member, and using the estimated temperature of the passage-defining member as the data representative of the temperature of the passage-defining member. In particular, for estimating the temperatures of the exhaust gases in passage-defining members, the exhaust gas temperature estimating means should preferably comprise means for sequentially estimating the temperatures of the passage-defining members which define the partial exhaust passageways using at least the estimated values of the temperatures of the exhaust gas in the partial exhaust passageways and data representative of an atmospheric temperature outside of the passage-defining members, and using the estimated temperatures of the passage-defining members as the data representative of the temperatures of the passage-defining members. The above arrangement holds true for the methods according to the first and second aspects, and the same process as the process of the exhaust gas temperature estimating means should preferably be carried out by the step of estimating the temperature of the exhaust gas. Similarly, with the recording mediums according to the first and second aspects, the exhaust gas temperature estimating program should preferably be a program for enabling the computer to carry out the same process as the process of the exhaust gas temperature estimating means.
By thus estimating the temperature of the passage-defining member together with the temperature of the exhaust gas, the data representative of the temperature of the passage-defining member can be acquired without using a temperature sensor, and hence the cost can be reduced. By using the estimated value of the temperature of the exhaust gas and the data representative of the atmospheric temperature for estimating the temperature of the passage-defining member, the temperature of the passage-defining member can be estimated in a manner taking into account a heat transfer between the passage-defining member and the exhaust gas flowing therein and a heat radiation from the passage-defining member into the atmosphere, and the temperature of the passage-defining member thus estimated is highly accurate.
The internal combustion engine is usually associated with an atmospheric temperature sensor for detecting an atmospheric temperature for the purpose of controlling operation of the internal combustion engine. A detected value from the atmospheric temperature sensor may be used as the above data representative of the atmospheric temperature.
For estimating the temperature of the passage-defining member in the vicinity of the location of the exhaust gas sensor, more specifically, the exhaust gas temperature estimating means should preferably comprise means for sequentially estimating a change in the temperature of the passage-defining member based on a thermal model in which a change per predetermined time in the temperature of the passage-defining member is expressed as including at least a temperature change component depending on the difference between the temperature of the exhaust gas in the vicinity of the location of the exhaust gas sensor and the temperature of the passage-defining member and a temperature change component depending on the difference between the temperature of the passage-defining member and the atmospheric temperature, and estimating the temperature of the passage-defining member by cumulatively adding the estimated value of the change in the temperature of the passage-defining member to an initial value set when the internal combustion engine has started to operate. The above arrangement holds true for the methods according to the first and second aspects, and the same process as the process of the exhaust gas temperature estimating means should preferably be carried out by the step of estimating the temperature of the exhaust gas. Similarly, with the recording mediums according to the first and second aspects, the exhaust gas temperature estimating program should preferably be a program for enabling the computer to carry out the same process as the process of the exhaust gas temperature estimating means.
For estimating the temperatures of the passage-defining members which define the respective partial exhaust passageways, more specifically, the exhaust gas temperature estimating means should preferably comprise means for sequentially estimating changes in the temperatures of the passage-defining members which define the partial exhaust passageways based on a thermal model in which changes per predetermined time in the temperatures of the passage-defining members are expressed as including at least temperature change components depending on the difference between the temperatures of the exhaust gas in the passage-defining members and the temperatures of the passage-defining members and temperature change components depending on the difference between the temperatures of the passage-defining members and the atmospheric temperature, and estimating the temperatures of the passage-defining members by cumulatively adding the estimated values of the changes in the temperatures of the passage-defining members to initial values set for the respective partial exhaust passageways when the internal combustion engine has started to operate. The above arrangement holds true for the methods according to the first and second aspects, and the same process as the process of the exhaust gas temperature estimating means should preferably be carried out by the step of estimating the temperature of the exhaust gas. Similarly, with the recording mediums according to the first and second aspects, the exhaust gas temperature estimating program should preferably be a program for enabling the computer to carry out the same process as the process of the exhaust gas temperature estimating means.
In the thermal model, a temperature change component depending on the difference between the temperature of the exhaust gas and the temperature of a passage-defining member refers to a temperature change component of the passage-defining member (a temperature change component in a location to be handled in the thermal model) which is caused by a heat transfer between the passage-defining member and the exhaust gas. A temperature change component depending on the difference between the temperature of the passage-defining member and the atmospheric temperature refers to a temperature change component of the passage-defining member (a temperature change component in a location to be handled in the thermal model) which is caused by a heat radiation from the passage-defining member into the atmosphere. Therefore, a change per given time in the temperature of the passage-defining member can accurately be determined based on the thermal model. It is then possible to determine an estimated value of the temperature of the passage-defining member with high accuracy by cumulatively adding the change in the temperature of the passage-defining member to an initial model that has been set at the time the internal combustion engine has started to operate, i.e., a predicted value of the temperature of the passage-defining member in a location to be handled in the thermal model at the time the internal combustion engine has started to operate. The temperature of the exhaust gas can hence be estimated accurately using the estimated value of the temperature of the passage-defining member.
A temperature change component depending on the difference between the temperature of the passage-defining member and the temperature of the exhaust gas can be determined from the latest estimated value (the latest one of already determined values) of the temperature of the passage-defining member and the latest estimated value (the latest one of already determined values) of the temperature of the exhaust gas. A temperature change component depending on the difference between the temperature of the passage-defining member and the atmospheric temperature can be determined from the latest estimated value of the temperature of the passage-defining member and the latest value of the data representative of the atmospheric temperature.
With any of the apparatus, the method, and the recording mediums according to the first and second aspects of the present invention, for estimating the temperatures of the exhaust gas in the respective partial exhaust passageways and the temperatures of the passage-defining members, if at least one of the partial exhaust passageways includes a catalyst for purifying the exhaust gas, as a passage-defining member which defines a portion of the exhaust passage, then the thermal model which corresponds to the passage-defining member including the catalyst should preferably comprise a model in which a change per predetermined time in the temperature of the passage-defining member which defines the partial exhaust passageway is expressed as the sum of at least a temperature change component depending on the difference between the temperature of the exhaust gas in the partial exhaust passageway and the temperature of the passage-defining member, a temperature change component depending on the difference between the temperature of the passage-defining member and the atmospheric temperature, and a temperature change component depending on the speed of the exhaust gas.
In the above thermal model, a temperature change component depending on the speed of the exhaust gas refers to a temperature change component of the catalyst (a passage-defining member) based on heating of the catalyst due to its own exhaust gas purifying action. Specifically, as the speed of the exhaust gas increases, the amount of the exhaust gas with which the catalyst reacts per given time increases, resulting in an increase in the amount of heat generated by the catalyst. Accordingly, the temperature change component of the catalyst based on its heating depends on the speed of the exhaust gas. Based on the thermal model, it is possible to estimate accurately a change per given time in the temperature of the passage-defining member which defines the partial exhaust passageway including the catalyst, thus increasing the accuracy of the estimated value of the temperature of the passage-defining member.
For estimating the temperature of the exhaust gas and the temperature of the passage-defining member by cumulatively adding a change per given time in the temperature to an initial value, the initial value should preferably be set depending on at least the atmospheric temperature and/or the engine temperature of the internal combustion engine when the internal combustion engine starts to operate. Thus, initial values of the temperature of the exhaust gas and the temperature of the passage-defining member can properly be set when the internal combustion engine starts to operate.
With the apparatus, the method, and the recording mediums according to the first and second aspects of the present invention (including those which do not estimate the temperature of the exhaust gas according to the second aspect), the exhaust gas sensor may comprise an O2 sensor disposed downstream of a catalytic converter for purifying the exhaust gas, for example. For well controlling the air-fuel ratio of the exhaust gas to keep the output voltage of the O2 sensor at a predetermined level in order for the catalytic converter to perform its desired exhaust gas purifying capability, the temperature of the active element of the O2 sensor should preferably be controlled at a predetermined target temperature equal to or higher than 750xc2x0 C., e.g., 800xc2x0 C.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.